Flux-trapped permanent magnets composed of superconducting material have been characterized as very incomplete Meissner effect magnets. This type of magnet is formed by applying a large magnetic field (beyond H.sub.c1) to a type II superconductor, and then turning off the external field. A portion of the field remains trapped inside the superconducting material. The trapped field is due to the persistent currents within the type II superconductor. These currents are microscopic vortex currents. The trapping mechanism occurs due to the pinning of the vortices. The pinning center is achieved by creating non-superconducting (normal) regions through impurities, inhomogeneities, or defects. A normal region may consist of tiny holes that are formed in the superconductor during its manufacture, or it may be subsequently etched to produce the holes. Photo-etching or plasma etching may be used to make a regular array of fine holes. Increased pinning forces at the edges of the normal regions tend to strongly trap the cores of the fluxolds in these regions. Trapped fields as high as 22400 Gauss at 4.degree. K. have been achieved. Multipole external applied field resulted in a multipole trapped field.
After the discovery of high transition temperature, T.sub.c, superconductors, practical trapped flux permanent magnets became more viable. This viability occurs since the high temperature-superconductor materials have extraordinarily high H.sub.c2 values and require only modest cost for refrigeration at 77.degree. K. This is a substantially lower cost than that of cooling to 4.degree. K. In spite of this economical advantage, some disadvantages are associated with the application of high T.sub.c materials in fabricating flux-trapped magnets. The disadvantages include (1) low H.sub.c1, (2) high flux creep, and (3) a large decreasing magnetization rate.